The present invention relates generally to a filter press type electrolyzer and, more particularly, to an electrolytic cell unit which is characterized by a partition for dispensing an electrolyte into adjacent electrolytic chambers.
Filter press type electrolyzers are widely used for inorganic material production by electrolysis, including chlorine and caustic soda production by brine electrolysis as well as for electrolysis of seawater, etc.
Among the filter press type electrolyzer used typically for brine electrolysis, there are two types, one a bipolar type built up of a stack of bipolar type electrolytic cell units partitioned by a cation exchange membrane, each unit including adjacent anode and cathode chambers electrically and mechanically joined to each other through a partition, and end electrode chambers attached and fixed as by hydraulic pressing on both ends thereof, each of said chambers having an anode or cathode on one side, and the other a monopolar type built up of a stack of anode and cathode chamber units having the same electrodes attached to the both sides of a picture frame form of electrode chamber frame partitioned by a cation exchange membrane and electrode chamber units attached to both ends thereof, each of said electrode chamber units having an anode or cathode on one side. Each electrode chamber unit of the monopolar type electrolyzer is provided with downcomers, ribs, etc. which reinforce the picture frame form of electrode chamber frame and serves to promote the circulation of an electrolyte. The electrodes are attached to these ribs, but there is usually no partition for separating the electrolyte.
On the other hand, each unit of the bipolar type electrolyzer is provided with partitions serving to separate the anode from the cathode chamber and to conduct an electrolytic current. The partitions for separating the anode from the cathode chamber are provided with an anode and a cathode. Depending on what electrolytic reactions are to take place, one of the anode and cathode chambers is exposed to an oxidizing environment and the other to a reducing environment. Especially in the case of brine electrolysis that is a typical electrolysis process making use of ion exchange membranes, chlorine is generated at the anode, while high concentrations of sodium hydroxide and hydrogen are formed at the cathode. Thus, a thin-film forming metal highly resistant to corrosion as by chlorine such as titanium, tantalum or zirconium or its alloy is used for the anode chamber. However, titanium absorbs hydrogen and embrittles in an atmosphere prevailing in the cathode chamber; in other words, titanium cannot be used for the cathode chambers, albeit highly resistant to corrosion.
For that reason, a ferrous metal such as iron, nickel or stainless steel or its alloy is used for the cathode chamber. Although electrical connection may be made by connecting electrode chambers to each other, each formed by a partition of metal material, no joint of practical strength can be obtained, even though titanium forming the anode chamber is directly joined to iron, nickel or stainless steel forming the cathode chamber as by welding, because titanium forms an intermetallic compound with the ferrous metal.
Thus, many proposals have been made for the bipolar type electrolyzer. For instance, Japanese Patent Publication No. 53-5880 discloses that the members forming the anode and cathode chambers are connected to each other by bolts passing through a partition formed of synthetic resin material.
Japanese Patent Publication No. 52-32866 discloses that a ferrous metal is explosively fused to titanium to form a sheet member serving as a partition, and both its sides are provided with ribs by welding and anodes and cathodes are welded to the ribs. Japanese Patent Publication No. 56-36231 teaches that a composite member is provided by joining together titanium and iron with copper between them, the titanium of the composite member is welded to the titanium of the anode-side partition of a bipolar type electrolytic cell unit, and the iron of the composite member is likewise welded to the cathode-side partition of a ferrous metal.
As mentioned above, various partitions are proposed for the bipolar type electrolyzer. However, since they all include partitions provided with ribs and electrodes welded or otherwise attached to the ribs, there are unavoidably voltage drops. In addition, special procedures must be used to join the cathode-side metal to the anode-side metal.
In order to solve such problems, Applicant has already proposed a bipolar type electrolyzer which includes electrolytic cell units, each formed by a pressed sheet of partitions having recesses (or grooves) and projections (or ribs) that are engaged with each other and electrodes joined to the projections, and which is simply assembled as well (see Japanese Provisional Patent Publication No. 3-249189 or Japanese Patent Application No. 2-45855).
In the case of an electrolytic reaction generating large amounts of gases, such as brine electrolysis by the ion exchange membrane process, zones in which the generated gases or liquids containing much bubbles remain stagnant are located upper part of electrode chambers. As well known in the art, the gas or air bubble-containing zones have an adverse influence on the ion exchange membranes during extended operation. In order to reduce the gas or bubble-containing zones, some improvement is made on where nozzles for releasing an electrolyte or the generated gases are to be located, or a gas-liquid separation chamber is located above the electrolytic cell unit, whereby the ion exchange membranes are prevented from coming into contact with the bubbles. If an electrolyzer having a large electrode area is operated while the current distribution in each electrode chamber remains uneven, then the performance of the electrolyzer is adversely affected; that is, local consumption of the electrodes occurs or local degradation of the ion exchange membranes takes place. Thus, where the electrodes and collector members are to be located is such designed as to make anode-partition-cathode-anode passages virtually equal to each other, thereby making the current distribution in each electrode chamber uniform.
Furthermore, it is attempted to reduce the concentration or temperature distribution of the electrolyte in each electrode chamber. Reducing the concentration or temperature distribution of the electrolyte is achieved by increasing the amount or rate of circulation of the electrolyte which is externally fed to the electrode chamber and discharged therefrom. However, increasing the amount of circulation needs a circulator of large size, and is not always effective as well in terms of making the concentration or temperature distribution of the electrolyte uniform.
In the case of an electrolytic cell unit including a pressed flat sheet, however, whatever measure is taken for where the electrolyte or the nozzle for releasing the gas generated is to be located, a region in which the gases remain stagnant occurs unavoidably upper portion of the electrolytic chamber.
Making the concentration or temperature of the electrolyte uniform may effectively be achieved by the uniform feeding of the electrolyte to the electrode chamber. However, never until now is an electrolyte-dispensing means used for electrolytic cell units making use of pressed sheets.
The section of the lower portion of a conventional electrolytic cell unit using a pressed sheet is shown in FIG. 12(A). As illustrated, there is an electrolytic cell frame 32 lower portion of the electrolytic cell unit generally shown at 31, and a partition 34 is attached to the frame 32 to form an electrode chamber 33. And an electrode 35 is mounted on the partition 34. Thus, the lower portion of the electrode chamber is constructed from the frame 32 formed of rigid material; in other words, some structural difficulty is encountered in providing means for dispensing the electrolyte uniformly.
The section of the upper portion of the electrolytic cell unit using a pressed sheet is shown in FIG. 12(B). As illustrated, the upper portion of the electrode chamber 33 of the electrolytic cell unit 31 is built up of an electrode chamber frame 32 formed of rigid material; that is, it is again structurally difficult to locate a gas-liquid separation chamber thereabove. Within the electrode chamber 33, there is left a space in which the electrode 35 is not located. This space is then sectioned by a parting member 36 formed of a metal sheet similar to the partition 34, thereby forming a gas-liquid separation chamber 38 provided with a passage 37 through which a gas-liquid mixture is introduced between said chamber 38 and the electrode chamber. However, problems with this arrangement are that the portion to be welded is so long and linear that this metal sheet forming the partition is distorted by welding, failing to provide an electrolytic cell unit to meet the mechanical accuracy demanded.